Except for Bitcoin, other currencies are government-accepted, a drawback of Bitcoin. Other currencies are traded daily, both small and large. Bitcoins are often used in large transactions. In addition, the price of a Bitcoin is much higher than other currencies, so if the opportunity develops, Bitcoin will rise to No. 1 in the world currency.
Bitcoin only used in exchanger and not many merchant in the world accepting bitcoin as payment. If government regulation allowing bitcoin for payment, bitcoin will much higher than now and maybe the rank will rise on top 3